Dr. Menahem Anderman, President of consultants Advanced Automotive Batteries, also is not convinced that Tesla engineers will continue to architect future battery packs and EV powertrains around the small, reliable, and thermodynamically efficient 18650, billions of which are produced annually (in various iterations) for the consumer electronics industry. Tesla is the only automotive OEM to use the 18650 cell.

“I don’t see other OEMs going to the 18650,” Dr. Anderman stated following a presentation on future battery trends at the 2014 SAE Hybrid & EV Symposium in La Jolla, CA, on February 13. He said the cost advantage Tesla realized when it first specified the 18650 cells for its original 2008 Roadster model has “eroded” compared with newly developed cylindrical, pouch, and prismatic cell configurations used across the auto industry, despite Tesla's increasing production volumes.

Around 7000 individual cells, coded NCR18650A by their supplier Panasonic, are used in each Model S pack. Rated at 3100 mA·h, the cells are based on lithium nickel-cobalt aluminum (NCA) chemistry and feature a proprietary cathode geometry developed by Panasonic and Tesla. Last October the two companies announced a battery-cell supply agreement through December 2017 (Panasonic also owns shares of Tesla Motors) which will cover the launch of the Model X in late 2014 and subsequent Model E vehicles.

But the automaker's official announcement did not specify a cell form factor, and a Tesla spokesperson contacted by Automotive Engineering following the announcement would not elaborate.

The Panasonic cells purchased by Tesla are specifically designed for the automaker and feature a Tesla-patented vent system within the end cap. Battery supplier sources who spoke anonymously estimate Tesla’s cell cost per kW·h to be less than $160.